The present invention relates to a gear case of an adjustment mechanism for a seat adjustment device of a motor vehicle, with the gear case being provided for the holding of mechanism elements of the adjustment mechanism, and the gear case being equipped with at least two case parts, wherein the case parts define two recesses for passage of a spindle of the adjustment mechanism, and the case parts can be joined together along a parting line to form the case, whereby at least two case parts in the region of the parting line of the case are provided with joint surfaces that are respectively cooperative when the case parts are joined together along the parting line. The invention also relates to an adjustment mechanism that includes such a gear case.
EP 1 068 093 B1 describes a gear case like that described immediately above. The gear case of EP 1 068 093 B1 holds a gear that is provided especially for a longitudinal seat adjuster. Such longitudinal seat adjusters serve the purpose of adjusting a motor vehicle seat in a longitudinal direction with respect to a floor structure of a vehicle. The adjustment is brought about by means of longitudinally moving an upper rail, on which the seat is located, with respect to an opposite lower rail. The gear case is attached to the upper rail, whereas the lower rail is fastened to the vehicle. With the gear, a rotary driving movement of an electric motor is transformed into the longitudinal adjustment movement.
With such gear cases, the absorbing of gear forces and also crash loads can cause problems. In order to make this possible with the simplest possible constructive design of the gear case, the gears would actually have to be quite massive in design. On the other hand, however, it is also desirable to integrate the gear cases between the upper and lower rails. For this reason there is a tendency to keep the size of the gear cases as small as possible. Consequently there is a conflict of goals with regard to the demands placed on a gear case.
With regard to the controllability of the gear forces and crash loads, the connection of the case parts is of particular relevance. In this connection, it is relatively easy to control pure compression forces, with which the case parts (typically two case parts) essentially press against one another. These forces can themselves be absorbed by means of the case parts, namely by means of surface pressure in the region of joint surfaces of the case parts. In this regard, the joint surfaces are the surfaces of the case parts that come into contact with each other due to the joining of the case parts at the joint. However, all other forces occurring in the region of the parting line of the case subject above all the connection of the case parts to the load. For this reason, in the state of the art, either comparatively massive or technically expensive connections are employed.
In EP 1 068 093 B1, which has already been named, plug and socket connections are to be provided for the solution of this problem, whereby by means of plastic deforming or for example a welding of the plug and socket connection a permanent and actually load bearing connection is generated between the case plates. However, in this connection the fact that for generation of the permanent connection cost-intensive equipment, such as for example laser welding equipment, is required can be perceived as a disadvantage. In addition, the possibility that the thermal energy used and/or the mechanical action on the plug and socket connections will damage gear elements cannot be ruled out.